2022-11-07_PERMIT FILE - M2022001 (7)

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Potential Slurry Wall and Mining Impacts to Local Groundwater Levels For all lined cells, a properly constructed slurry wall will tend to isolate these cells from the surrounding alluvial groundwater table. The liner around these cells could cause"mounding"of groundwater(increase in groundwater elevation) on the upgradient side (southeast) of the lined cells and a potential "shadow effect" (reduction in groundwater level) on the downgradient side (northwest) of the mine. Because the liner will tend to isolate these cells from the surrounding groundwater table, the effects of dewatering when mining lined cells will tend to not extend beyond the liner. Any mounding effect on the upgradient side of the site (south and southwest) is anticipated to be on the order of a few feet or less and will dissipate with distance from the mine. Similarly, shadowing effects will be on the order of a few feet and will dissipate with distance from the mine. The shadowing effects will be minimized by the presence of the South Platte River to the northwest and the Western Mutual Ditch that runs between Cells 5A and 513 and the Farmers Independent Ditch which runs southeast of the site. Dewatering of the unlined cells (Cells 1 and 2) will result in decreases in water levels around these cells. Since there are no wells permitted within 600' of the unlined cells, the effects of dewatering the unlined cells will be minimal. Area Wells A review of the permitted wells on file with the State Engineer's Office (SEO), Division of Water Resources (DWR) indicates that there are nineteen permitted pumping wells within 600 feet of the permit boundary. All of these wells are screened in the alluvium. None of these wells are within 600 feet of the unlined cells (Cells 1 and 2). The well locations and applicants are shown on Figure G-2 attached at the end of this section. Groundwater Level Monitoring and Mitigation Plan Dewatering during mining of Cells 1 and 2 is unlikely to affect any wells in the area. However, if the miner receives a complaint,the following mitigation plan will be implemented. The site monitoring wells will be measured monthly to identify potential changes in alluvial groundwater flow or elevation associated with mining and reclamation activities. Baseline data will be collected prior to dewatering or construction of the slurry walls. Baseline data will be collected from the monitoring program will provide a range of relative water levels associated with pre-mining groundwater conditions. Experience at other mines in similar geologic settings has found that groundwater levels tend to fluctuate being highest in the summer irrigation season and lowest in the winter and early spring. The monthly measurements will be tabulated and included with the DRMS annual report for the site. If, during mining or reclamation, the relative seasonal groundwater elevation at monitoring wells 5 or 6 show mounding of more than two (2)feet, and the condition was not observed during baseline monitoring, or if the miner receives a complaint from any well owner within 600 feet of the site boundary, then the miner will evaluate the cause and take action within 7 days and notify the DRMS. After the DRMS has been notified, the miner will review the data and available information and submit a report to the DRMS within 30 days. The evaluation will include discussions with the well owner who has contacted the miner regarding a concern and review of baseline data from the well and vicinity to evaluate whether changes may be due to seasonal variations, climate, mining, slurry wall lining or other factors. The report will identify the extent of potential or actual impacts associated with the changes. If the extent of Red Tierra Equities, LLC—Section 20 Mine—MLRB 112 Permit Application Exhibit G-4